Most automotive internal combustion engines have a coolant system which includes fluid conduits within the engine and adjacent the engine, and a heat exchanger through which coolant liquid flows.
For the protection of the internal combustion engine against overheating, an alarm, audible, and/or visual, to the operator should be activated if the temperature of the engine becomes excessive.
One major consideration in the protection of an internal combustion engine is that the coolant fluid in the coolant system must remain substantially in liquid form and should not be permitted to boil. The boiling point of the coolant liquid depends upon the composition thereof and also depends upon the pressure applied to the coolant liquid within the coolant system.
A coolant system of an internal combustion engine usually is a closed system in which a pressure cap closes the passage through which the coolant liquid is introduced into the coolant system. The pressure cap is designed to maintain a predetermined operating pressure within the coolant system. If a predetermined operating pressure in the coolant system could always be precisely maintained, the problems involved with regard to protection of the engine against excessive temperatures would be significantly reduced. If a predetermined operating pressure were always maintained in the coolant system, monitoring of the temperature of the engine would be the principal requirement for protection of the engine.
However, as a practical matter, the pressure in the coolant system cannot be properly or effectively controlled. This is due to the fact that the pressure cap is customarily one which has a pressure tolerance range. Also, an aging pressure cap permits a change in the operating pressure maintained in a coolant system. Furthermore, an aging coolant system becomes increasingly subject to leakage.
Most engine protection devices sense only the temperature of the engine, and a temperature alarm condition is established based upon an anticipated operating pressure within the coolant system. In such systems a temperature alarm may be energized at a time in which temperature conditions do not justify an alarm, or an alarm may not be energized at a time in which the engine is subjected to damage by excessive heat.
A coolant system which maintains less than an expected operating pressure permits the coolant liquid to boil at a temperature less than that for which the danger signal is designed to operate. Under such conditions, the coolant liquid may boil away and be lost from the coolant system without causing the alarm signal to be energized.
For these reasons, inter alia, devices which have been designed to protect an internal combustion engine against overheating have not been effective.
Thus, it is understood that in order to properly protect an internal combustion engine against overheating, it is necessary to sense both the temperature and the pressure within the coolant system of the internal combustion engine.
It is an object of this invention to provide a switch unit for protection of an internal combustion engine in which the switch unit senses both the temperature and pressure of the liquid in the coolant system and which operates as a function of a combination of the temperature and pressure conditions of the liquid within the coolant system.
Another object of this invention is to provide such a switch unit which is capable of operating and compensating as a function of both the temperature and pressure of a specific liquid in the coolant system.
Another object of this invention is to provide such a switch unit which has relatively long life and which may be produced at relatively low costs.
Other objects and advantages of this invention reside in the construction of parts, the combination thereof, the method of production and the mode of operation of the switch unit as will become more apparent from the following description.